Feedwater Heaters

Question 1

What are the indications of a stuck open drain(dump) valve?

Answer 1

Indications:

• FW heater low level
• Decrease in FW heater pressure
• Decrease in FW temperature on the affected FW heater with a possible overall FW temperature reduction
• Decrease in generator output due to higher extraction steam flows to the FW heaters and a possible decrease in main condenser vacuum due to extraction steam going directly to the main condenser
• Increase in Rx power due to colder FW temperature being injected into the Rx core

Question 2

How do Feedwater Heater drains operate during startup?

Answer 2

U1

< 280 MWe

• Insufficient driving pressure to permit the 8th stage heater to drain to 10th stage heater
• 8th stage heater level control system allows water to rise until high level setpoint is reached
• High level drain valve to main condenser opens & controls heater level

> 280 MWe
- Sufficient driving force to allow 8th stage heater to drain to 10th stage heater

U2
< 400 MWe
- 7th stage FW heater drain bypasses 8th stage FW heater & drains to 10th stage FW heater
- 8th stage FW heater drains directly to main condenser
- Necessary since difference in elevation b/w 8th & 10th stage FW heaters is enough to prevent sufficient driving head for drain flow

> 400 MWe
7th stage FW heater drains to 8th stage FW heater

Question 3

What are the power supplies for the feedwater heater drain pumps (Unit 1 only)?

Answer 3

Unit 1 ONLY:

Heater Drain Pumps A/B (600 VAC “A” & “B”)

Question 4

What is the arrangement of the FW heaters for Unit 1 and Unit 2?

Answer 4

Unit 1:
5th stage -> 7th stage -> 8th stage -> 10th stage -> 12th stage -> Drain Cooler -> Drain Pump -> Main Condenser

Unit 2:
4th stage -> 6th stage -> 7th stage -> 8th stage -> 10th Stage -> 12th stage -> Drain cooler -> Main Condenser

Question 5

What happens to the Extraction Non-return (ENR) check valves on a turbine trip, and what do they protect against?

Answer 5

Receive control signals from EHC to ensure these valves close on turbine trips to protect turbine from overspeeding.

Question 6

When are the heater drain pumps placed/removed from service for Unit 1?

Answer 6

Placed in service @ ≥ 200 GMWe. Removed from service @ turbine load < 80 GMWe.

Question 7

What happens to the feed water heater isolation/control valves on a high level in a given feedwater heater?

Answer 7

• High level alarms & Heater trouble alarm (U2 only)
• LCV to the next lower heater opens further
• High level dump valve to the main condenser opens
• Upstream heater LCV (on high pressure heater) closes
• Extraction steam isolation & ENR valves for affected heater close & Extraction Bypass valve will open, if level reaches the Hi level (Hi-Hi U1) in heater

Question 8

What actions are required on a loss of feedwater heating?

Answer 8

Per 34AB-N21-001-2, Loss of Feedwater
Action:
- If final feed water temp 10° less than standard track per 34SV-SUV-020-0
- Maintain Rx Pwr >1% less than pre-event level using Fast Lower (3%-5%) on master controller P603
- If Fuel Leakers, >10° below pre-event level, If no Fuel Leakers >20°
- Using recirc reduce power > 20% of pre-event level or ≤ 65% whichever is greater
- If in Immediate Exit Region or rods needed to continue power reduction
Insert rods if insert limits 20 to 00
If not, reduce core flow <55% then insert rods
If final feedwater temp unacceptable region, continued operation not allowed due to thermal limit analysis bounding assumptions being violated.
Restore w/i 2 hours or
Power reduced < 24% w/i 4 hours